1. Field of the Invention
The present invention relates to a controller for a DC brushless motor which can detects the rotor angle of a DC brushless motor without using a rotor position detecting sensor and control the operation of the motor.
2. Description of the Related Art
In order to obtain a desired torque by energizing a DC brushless motor, a voltage needs to be applied to an armature in an appropriate phase which corresponds to an electrical angle (hereinafter, referred to as a rotor angle) of a rotor having magnetic poles. With a view to reducing costs for a DC brushless motor and a motor drive unit by omitting a position detecting sensor for detecting the rotor angle, there have been proposed many methods for detecting the rotor angle with using no position detecting sensor.
For example, Japanese Patent Unexamined Publication Nos. Hei. 10-323099 and Hei. 11-332279 describe methods for detecting the rotor angle of a DC brushless motor in a motor control apparatus for controlling such a DC brushless motor by a so-called dq coordinate system in which method an estimation alternating current signal voltage is applied in a direction of one of axes to thereby generate on the other axis side a current, by which the rotor angle is detected.
In addition, the inventor et al. of the present invention proposed, in US 2002/0149335A1, a rotor angle detecting apparatus for detecting the rotor angle using no position detecting sensor. In the rotor angle detecting apparatus, when a high-frequency voltage is imposed on a drive voltage which is applied to three phase armatures of a salient pole-type DC brushless motor, a detection value of a current flowing to a first-phase armature and a detection value of a current flowing to a second-phase armature of the three phase armatures and a high-frequency component corresponding to the high-frequency voltage are used to calculate a sine reference value corresponding to a sine value of an angle which is twice the rotor angle of the motor and a cosine reference value corresponding to a cosine value of an angle which is twice the rotor angle of the motor.
Then, the rotor angle can be detected based on the sine reference value and the cosine reference value with good initial follow-up characteristics and with being affected little by motor parameters.
However, when imposing the high-frequency voltage on the drive voltage in order to detect the rotor angle, there may occur a case where irksome noise is generated from the motor. In addition, in order to impose an alternating current signal voltage on a drive voltage, the capacity of an inverter for outputting a drive voltage to the motor needs to be increased. Furthermore, in order to prevent the interference of a response from the motor current feedback control system with a response from the rotor angle detection system, while the response from the current feedback control system needs to be separated from the response from the rotor angle detection system by a low-pass filter, there may be caused a risk that the provision of the low-pass filter deteriorates the response from the current feedback system.